An electronic apparatus, such as a digital camera, includes a solid-state imaging device. Examples of the solid-state imaging device include a CMOS (complementary metal oxide semiconductor) image sensor and a CCD (charge coupled device) image sensor.
In a solid-state imaging device, a pixel array area having a plurality of pixels arranged in a matrix is provided on a surface of a semiconductor substrate. Each of the plurality of pixels is provided with a photoelectric converter. The photoelectric converter is, for example, a photodiode. A light receiving surface of the photodiode receives light incident thereon via an optical system provided separately from the imaging device, and signal charge is produced in a photoelectric conversion process.
Among a variety of solid-state imaging devices, a CMOS image sensor is so configured that each pixel includes a plurality of transistors as well as the photoelectric converter. The plurality of transistors read the signal charge produced by the photoelectric converter and output the signal charge in the form of an electric signal to a signal line.
A semiconductor device, such as a solid-state imaging device, is provided with a pad electrode, which is provided to electrically connect the semiconductor device to an external component. For example, the semiconductor device is electrically connected to a board substrate, a semiconductor package, a semiconductor chip, or any other external component via the pad electrode.
The pad electrode is made, for example, of aluminum (Al). The pad electrode is alternatively made of an aluminum alloy containing silicon (Si), copper (Cu), and other elements.
For example, the semiconductor device, such as a solid-state imaging device, is electrically connected to an external device via the pad electrode by using a connection means, such as gold (Au)-based wire bonding and tin (Sn)-based solder reflow (see Japanese Patent Nos. 3,158,466 and 3,959, 710, for example).
When a contaminant is present on the surface of the pad electrode, electrical connection failure between the semiconductor device and an external device may occur in some cases. The electrical connection failure may cause the solid-state imaging device not to operate normally, for example, to malfunction and eventually stop operating. To avoid such a situation, the surface of the pad electrode is so cleaned that any contaminant is removed.
For example, when layers provided on the pad electrode made of aluminum are dry etched by using a fluorine (F)-based etching gas, the fluorine (F) may become a contaminant on the pad electrode in some cases. To remove the fluorine (F) left on the pad electrode, it has been proposed to clean the surface of the pad electrode with an organic amine-based chemical solution (see “Investigation and Failure Analysis of “Flower-like” Defects on Microchip Aluminum Bondpads in Wafer Fabrication,” ICSE2006 Proc. 2006, pp. 626-629, for example).
Further, the pad metal of the pad electrode may melt and corrode, resulting in malfunction of the device in some cases. To avoid such a situation, it has been proposed to electrically connect the semiconductor device to an external device via the pad electrode and then form a carbon film that covers the semiconductor device, the external device, and a wiring line that connects them to each other (see JP-A-3-83365 and JP-A-62-12163, for example).